This invention relates to waterborne paints or coatings, and is more particularly directed to an aqueous coating composition of applying as a temporary protective coating which produces a film that when dry is insensitive to water or weather, but can be removed with an ammonia gel or other alkali solution.
There are several applications where temporary, but durable protective paints or coatings would be desirable. For example, if military equipment is to be used temporarily in an arctic or other environment, it may be desirable to camouflage the equipment for that environment, and then remove the camouflage at the end of the operation or exercise. It is also desirable to coat equipment with a durable but removable film if the equipment is to be used in a contaminant environment, so that any contaminants can be taken off with the protective coating.
At present, temporary camouflage paints have not been sufficiently water-insensitive to provide acceptable durability, or else have been extremely difficult to remove when no longer needed.
The nature of many waterborne paints or coatings composition, is that there are tiny particles of a polymer vehicle that are dispersed in water to form a suspension. The polymer itself is colorless, and pigments are added to achieve the desired cover of the visible surface to be coated. These pigments are solid particle colorants and said particle flattening agents. In order to provide effective coating, the particles of pigment must disperse into the vehicle, i.e., must "wet" and surround themselves with the particles of suspended polymer.
For removable coatings, an acrylic copolymer is suitable for use as the vehicle, because although waterborne until applied, it becomes insensitive to water or weather when dried but can be re-sensitized to moisture by application of an alkali solution, such as an ammonia solution or an ammonia gel.
Unfortunately, pigments, i.e., solid particles, do not disperse well in water or the acrylic resin particles, and thus an acrylic based paint or coating requires a surface-active agent to wet the pigments relative to the vehicle. However, after the composition has been applied and dried into a film, conventional surfactants remain water-sensitive and will tend to redissolve or wash away in the presence of moisture.